High-data-rate supplemental channel for CDMA telecommunications system

ABSTRACT

A novel and improved method for implementing a high-transmission-rate over-the-air interface is described. A transmit system provides an in-phase channel set and a quadrature-phase channel set. The in-phase channel set is used to provide a complete set of orthogonal medium rate control and traffic channels. The quadrature-phase channel set is used to provide a high-rate supplemental channel and an extended set of medium rate channels that are orthogonal to each other and the original medium rate channels. The high-rate supplemental channel is generated over a set of medium rate channels using a short channel code. The medium rate channel are generated using a set of long channel codes.

This application is a division of Ser. No. 08/784,281 filed Jan. 15,1997.

BACKGROUND OF THE INVENTION

I. Field of the Invention

The present invention relates to wireless telecommunications. Moreparticularly, the present invention relates to a novel and improvedmethod for implementing a high-transmission-rate over-the-air interface.

II. Description of the Related Art

The IS-95 standard from the Telecommunications Industry Association(TIA), and its derivatives such as IS-95A and ANSI J-STD-008 (referredto herein collectively as IS-95), define an over-the-air interfacesuitable for implementing a bandwidth-efficient digital cellulartelephone system. To this end, IS-95 provides a method for establishingmultiple radio frequency (RF) traffic channels, each having a datatransmission rate of up to 14.4 kilobits per second. The trafficchannels can be used for conducting voice telephony or for conductingdigital data communications including small file transfer, electronicmail, and facsimile.

While 14.4 kilobits per second is adequate for these types of lower datarate applications, the increasing popularity of more data intensiveapplications such as worldwide web and video conferencing has created ademand for much higher transmission rates. To satisfy this new demand,the present invention is directed towards providing an over-the-airinterface capable of higher transmission rates.

FIG. 1 illustrates a highly simplified digital cellular telephone systemconfigured in a manner consistent with the use of IS-95. Duringoperation, telephone calls and other communications are conducted byexchanging data between subscriber units 10 and base stations 12 usingRF signals. The communications are further conducted from base stations12 through base station controllers (BSC) 14 and mobile switching center(MSC) 16 to either public switch telephone network (PSTN) 18, or toanother subscriber unit 10. BSC's 14 and MSC 16 typically providemobility control, call processing, and call routing functionality.

In an IS-95 compliant system, the RF signals exchanged betweensubscriber units 10 and base stations 12 are processed in accordancewith code division multiple access (CDMA) signal processing techniques.The use of CDMA signal processing techniques allows adjacent basestations 12 to use the same RF bandwidth which, when combined with theuse of transmit power control, makes IS-95 more bandwidth efficient thanother cellular telephone systems.

CDMA processing is considered a "spread spectrum" technology because theCDMA signal is spread over a wider amount of RF bandwidth than isgenerally used for non-spread spectrum systems. The spreading bandwidthfor an IS-95 system is 1.2288 MHz. A CDMA-based digital wirelesstelecommunications system configured substantially in accordance withthe use of IS-95 is described in U.S. Pat. No. 5,103,450 entitled"SYSTEM AND METHOD FOR GENERATING SIGNAL WAVEFORMS IN A CDMA CELLULARTELEPHONE SYSTEM," assigned to the assignee of the present invention andincorporated herein by reference.

It is anticipated that the demand for higher transmission rates will begreater for the forward link than for the reverse link because a typicaluser is expected to receive more data than he or she generates. Theforward link signal is the RF signal transmitted from a base station 12to one or more subscriber units 10. The reverse link signal is the RFsignal transmitted from subscriber unit 10 to a base station 12.

FIG. 2 illustrates the signal processing associated with an IS-95forward link traffic channel, which is a portion of the IS-95 forwardlink signal. The forward link traffic channel is used for thetransmission of user data from a base station 12 to a particularsubscriber unit 10. During normal operation, the base station 12generates multiple forward link traffic channels, each of which is usedfor communication with a particular subscriber unit 10. Additionally,the base station 12 generates various control channels including a pilotchannel, a sync channel, and a paging channel. The forward link signalis the sum of the traffic channels and control channels.

As shown in FIG. 2, user data is input at node 30 and processed in 20millisecond (ms) blocks called frames. The amount of data in each framemay be one of four values with each lower value being approximately halfof the next higher value. Also, two possible sets of frame sizes can beutilized, which are referred to as rate set one and rate set two.

For rate set two the amount of data contained in the largest, or"full-rate," frame corresponds to a transmission rate of 13.35 kilobitsper second. For rate set one the amount of data contained in the fullrate frame corresponds to a transmission rate of 8.6 kilobits persecond. The smaller sized frames are referred to as half-rate,quarter-rate, and eighth-rate frames. The various frame rates are usedto adjust for the changes in voice activity experienced during a normalconversation.

CRC generator 36 adds CRC data with the amount of CRC data generateddependent on the frame size and rate set. Tail byte generator 40 addseight tail bits of known logic state to each frame to assist during thedecoding process. For full-rate frames, the number of tail bits and CRCbits brings the transmission rate up to 9.6 and 14.4 kilobits per secondfor rate set one and rate set two.

The data from tail byte generator 40 is convolutionally encoded byencoder 42 to generate code symbols 44. Rate 1/2, constraint length (K)9, encoding is performed.

Puncture 48 removes 2 of every 6 code symbols for rate set two frames,which effectively reduces the encoding performed to rate 2/3. Thus, atthe output of puncture 48 code symbols are generated at 19.2 kilosymbolsper second (ksps) for both rate set one and rate set two full-rateframes.

Block interleaver 50 performs block interleaving on each frame, and theinterleaved code symbols are modulated with a Walsh channel code fromWalsh code generator 54 generating sixty-four Walsh symbols for eachcode symbol. A particular Walsh channel code W_(i) is selected from aset of sixty-four Walsh channel codes and typically used for theduration of an interface between a particular subscriber unit 10 and abase station 12.

The Walsh symbols are then duplicated, and one copy is modulated with anin-phase PN spreading code (PN_(I)) from spreading code generator 52,and the other copy is modulated with a quadrature-phase PN spreadingcode (PN_(Q)) from spreading code generator 53. The in-phase data isthen low-pass filtered by LPF 58 and modulated with an in-phasesinusoidal carrier signal. Similarly, the quadrature-phase data islow-pass filtered by LPF 60 and modulated with a quadrature-phasesinusoidal carrier. The two modulated carrier signals are then summed toform signal s(t) and transmitted as the forward link signal.

SUMMARY OF THE INVENTION

The present invention is a novel and improved method for implementing ahigh-transmission-rate over-the-air interface. A transmit systemprovides an in-phase channel set and a quadrature-phase channel set. Thein-phase channel set is used to provide a complete set of orthogonalmedium rate control and traffic channels. The quadrature-phase channelset is used to provide a high-rate supplemental channel and an extendedset of medium rate channels that are orthogonal to each other and theoriginal medium rate channels. The high-rate supplemental channel isgenerated over a set of medium rate channels using a short channel code.The medium rate channel are generated using a set of long channel codes.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, objects, and advantages of the present invention willbecome more apparent from the detailed description set forth below whentaken in conjunction with the drawings in which like referencecharacters identify correspondingly throughout and wherein:

FIG. 1 is a block diagram of a cellular telephone system;

FIG. 2 is a block diagram of the forward link signal processingassociated with the IS-95 standard;

FIG. 3 is a block diagram of a transmit system configured in accordancewith one embodiment of the invention;

FIGS. 4A-4D is a list of the set of 64-symbol Walsh codes and associatedindexes used in a preferred embodiment of the invention.

FIG. 5 is a block diagram of the channel coding performed in accordancewith one embodiment of the invention;

FIG. 6 is a block diagram of a receive system configured in accordancewith one embodiment of the invention; and

FIG. 7 is a block diagram of a decoding system configured in accordancewith one embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 3 is a block diagram of a transmit system configured in a mannerconsistent with use of the invention. Typically, the transmit systemwill be used to generated the forward link signal in a cellulartelephone system and therefore would be incorporated into a base station12. In the exemplary configuration shown, the transmit system generatesa forward link signal that includes a complete set of IS-95, or mediumrate, channels as well as a high-speed supplemental channel.Additionally, in the embodiment described, an extended set of IS-95channels is provided. Alternative embodiments of the invention couldprovide more than one high-speed supplemental channel, or not providethe use of an additional set of IS-95 channels, or both. Also, whileproviding IS-95 channels is preferred, other embodiments of theinvention may incorporate other channel types and processing protocols.

In the exemplary embodiment provided, the transmit system provides anin-phase channel set 90 and a quadrature-phase channel set 92. Thein-phase channel set 90 is used to provide the complete set oforthogonal IS-95 control and traffic channels. Orthogonal channel to notinterfere with one another when transmitted via the same path. Thequadrature-phase channel set 92 is used to provide a high-ratesupplemental channel and an extended set of IS-95 channels that areorthogonal to each other and the original IS-95 channels. In thepreferred embodiment of the invention, all the signals and data shown inFIG. 3 are formed by positive and negative integer values represented bybinary digital data or voltages, which correspond to a logic low and alogic high, respectively.

For the in-phase channel set 90, IS-95 control channel system 100performs various functions associated with one of the standard IS-95control channels including encoding and interleaving, the processing ofwhich is described in IS-95 incorporated herein by reference. In thiscase, since the Walsh₁ channel code is used, the processing will be inaccordance with the use of a paging channel. The resulting code symbolsfrom IS-95 control channel system 100 are modulated with a Walsh codefrom Walsh, generator 102 by multiplier 104. The Walsh generators 102are used to generate the orthogonal in-phase channels.

Walsh generator 102 repeatedly generates a Walsh code of index 1(Walsh₁) from a set of Walsh codes of indexes 0 to 63 (Walsh₀₋₆₃). FIGS.4A-4D is a list of the set of 64-symbol Walsh codes and associatedindexes used in a preferred embodiment of the invention. A Walsh chipcorresponds to a Walsh symbol and a Walsh chip value of 0 corresponds toa positive (+) integer while a Walsh chip value of 1 corresponds to anegative (-) integer. Under IS-95 Walsh, code corresponds to the pagingchannel. The Walsh symbols generated by modulation with the Walsh, codeare gain adjusted by channel gain 108 (2).

The pilot channel is generated by gain adjusting a positive 1 valueusing channel gain 108 (1). No encoding is performed for the pilotchannel in accordance with IS-95, as the Walsh₀ code used for the pilotchannel is all plus 1 values, and therefore equivalent to no modulationat all.

Additional control channels are generated in similar fashion usingadditional IS-95 control channel systems, additional Walsh generators,and additional channel gains (all not shown). Such control channelsinclude a synchronization channel, which is modulated with the Walsh₃₂code. The processing associated with each type of IS-95 control channelis described in IS-95.

The processing associated with one of the IS-95 traffic channels in thein-phase channel set is illustrated with IS-95 traffic channel system110, which performs various functions associated with an IS-95 trafficchannel including convolutional encoding and interleaving as describedabove to generate a sequence of symbols at 19.2 kilosymbols per second.The code symbols from IS-95 traffic channel system 110 are modulatedwith the 64-symbol Walsh₆₃ code from Walsh₆₃ generator 112 by multiplier114 to generate a sequence of symbols at 1.2288 Megasymbols per second.The Walsh symbols from multiplier 114 are gain adjusted by gain adjust108 (64).

The outputs of all gain adjusts including gain adjusts 108 (1)-(64) aresummed by summer 120 generating in-phase data D_(I). Each gain adjust108 increases or decreases the gain of the particular channel with whichit is associated. The gain adjust can be performed in response to avariety of factors including power control commands from the subscriberunit 10 processing the associated channel, or to differences in the typeof data being transmitted over the channel. By keeping the transmitpower of each channel at the minimum necessary for proper communication,interference is reduced and the total transmit capacity increased. Inone embodiment of the invention, gain adjusts 108 are configured by acontrol system (not shown) which could take the form of amicroprocessor.

Within quadrature-phase channel set 92, an extended set of 64-2^(N)IS-95 traffic channels are provided using IS-95 channel systems 124. Nis a integer value based on the number of Walsh channels allocated forthe supplemental channel and is described in greater detail below. Eachcode symbols from the IS-95 channel systems 124 (2)-(64-2^(N)) ismodulated with a Walsh code from Walsh generators 126 by multipliers128, except for IS-95 traffic channel system 124 (1), which is placed onWalsh₀ channel, and therefore does not require modulation.

To provide the high-rate supplemental channel, supplemental channelsystem 132 generates code symbols at a rate R_(S), which is 2^(N) timesthat of a full-rate IS-95 traffic channel. Each code symbol is modulatedwith a supplemental Walsh code (Walsh_(S)) from supplemental Walsh codegenerator 134 using multiplier 140. The output of multiplier 140 is gainadjusted by gain adjust 130. The outputs of the set of gain adjusts 130are summed by summer 150 yielding quadrature-phase data D_(Q). It shouldbe understood that the extended set of IS-95 traffic channel could becompletely or partially replaced with one or more additionalsupplemental channels.

The processing performed by supplemental channel system 132 is describedin greater detail below. The Walsh_(S) code generated by supplementalWalsh code generator 134 depends the number of Walsh codes allocated forthe high-rate supplemental channel in quadrature-phase channel set 92.In the preferred embodiment of the invention, the number of Walshchannels allocated for the high-rate supplemental channel can be anyvalue 2^(N) where N={2, 3, 4, 5, 6}. The Walsh_(S) codes are 64/2^(N)symbols long, rather than the 64 symbols used with the IS-95 Walshcodes. In order for the high-rate supplemental channel to be orthogonalto the other quadrature-phase channels with 64-symbol Walsh codes, 2^(N)of the possible 64 quadrature-phase channels with 64-symbol Walsh codescannot be used for the other quadrature-phase channels. Table I providesa list of the possible Walsh_(S) codes for each value of N and thecorresponding sets of allocated 64-symbol Walsh codes.

                                      TABLE I                                     __________________________________________________________________________    N  Walsh.sub.i       Allocated 64-Symbol Walsh Codes                          __________________________________________________________________________    2  +, +, +, +, +, +, +, +, +, +, +, +, +, +, +, +                                                  0, 16, 32, 48                                               +, -, +, -, +, -, +, -, +, -, +, -, +, -, +, -                                                  1, 17, 33, 49                                               +, +, -, -, +, +, -, -, +, +, -, -, +, +, -, -                                                  2, 18, 34, 50                                               +, -, -, +, +, -, -, +, +, -, -, +, +, -, -, +                                                  3, 19, 35, 51                                               +, +, +, +, -, -, -, -, +, +, +, +, -, -, -, -                                                  4, 20, 36, 52                                               +, -, +, -, -, +, -, +, +, -, +, -, -, +, -, +                                                  5, 21, 37, 53                                               +, +, -, -, -, -, +, +, +, +, -, -, -, -, +, +                                                  6, 22, 38, 54                                               +, -, -, +, -, +, +, -, +, -, -, +, -, +, +, -                                                  7, 23, 39, 55                                               +, +, +, +, +, +, +, +, -, -, -, -, -, -, -, -                                                  8, 24, 40, 56                                               +, -, +, -, +, -, +, -, -, +, -, +, -, +, -, +                                                  9, 25, 41, 57                                               +, +, -, -, +, +, -, -, -, -, +, +, -, -, +, +                                                  10, 26, 42, 58                                              +, -, -, +, +, -, -, +, -, +, +, -, -, +, +, -                                                  11, 27, 43, 59                                              +, +, +, +, -, -, -, -, -, -, -, -, +, +, +, +                                                  12, 28, 44, 60                                              +, -, +, -, -, +, -, +, -, +, -, +, +, -, +, -                                                  13, 29, 45, 61                                              +, +, -, -, -, -, +, +, -, -, +, +, +, +, -, -                                                  14, 30, 46, 62                                              +, -, -, +, -, +, +, -, -, +, +, -, +, -, -, +                                                  15, 31, 47, 63                                           3  +, +, +, +, +, +, +, +                                                                          0, 8, 16, 24, 32, 40, 48, 56                                +, -, +, -, +, -, +, -                                                                          1, 9, 17, 25, 33, 41, 49, 57                                +, +, -, -, +, +, -, -                                                                          2, 10, 18, 26, 34, 42, 50, 58                               +, -, -, +, +, -, -, +                                                                          3, 11, 19, 27, 35, 43, 51, 59                               +, +, +, +, -, -, -, -                                                                          4, 12, 20, 28, 36, 44, 52, 60                               +, -, +, -, -, +, -, +                                                                          5, 13, 21, 29, 37, 45, 53, 61                               +, +, -, -, -, -, +, +                                                                          6, 14, 22, 30, 38, 46, 54, 62                               +, -, -, +, -, +, +, -                                                                          7, 15, 23, 31, 39, 47, 55, 63                            4  +, +, +, +        0, 4, 8, . . ., 60                                          +, -, +, -        1, 5, 9, . . ., 61                                          +, +, -, -        2, 6, 10, . . ., 62                                         +, -, -, +        3, 7, 11, . . ., 63                                      5  +, +              0, 2, 4, . . ., 62                                          +, -              1, 3, 5, . . ., 63                                       6  +                 0, 1, 2, . . ., 63                                       __________________________________________________________________________

The + and - indicate a positive or negative integer value, where thepreferred integer is 1. As is apparent, the number of Walsh symbols ineach Walsh_(S) code varies as N varies, and in all instances is lessthan the number of symbols in the IS-95 Walsh channel codes. Thus, thesupplemental channel is formed using a short Walsh channel code and theIS-95 channels are formed using longer Walsh channel codes. Regardlessof the length of the Walsh_(S) code, in the described embodiment of theinvention the symbols are applied at a rate of 1.2288 Megachips persecond (Mcps). Thus, shorter length Walsh_(S) codes are repeated moreoften.

Data channels D_(I) and D_(Q) are complex multiplied, as the first realand imaginary terms respectively, with spreading codes PN_(I) andPN_(Q), as the second real and imaginary terms respectively, yieldingin-phase (or real) term X_(I) and quadrature-phase (or imaginary) termX_(Q). Spreading codes PN_(I) and PN_(Q) are generated by spreading codegenerators 152 and 154. Spreading codes PN_(I) and PN_(Q) are applied at1.2288 Mcps. Equation (1) illustrates the complex multiplicationperformed.

    (X.sub.I +jX.sub.Q)=(D.sub.I +jD.sub.Q)(PN.sub.I +jPN.sub.Q)(1)

In-phase term X_(I) is then low-pass filtered to a 1.2288 MHz bandwidth(not shown) and upconverted by multiplication with in-phase carrierCOS(ω_(c) t). Similarly, quadrature-phase term X_(Q) is low-passfiltered to a 1.2288 MHz bandwidth (not shown) and upconverted bymultiplication with quadrature-phase carrier SIN(ω_(c) t). Theupconverted X_(I) and X_(Q) terms are summed yielding forward linksignal s(t).

The complex multiplication allows quadrature-phase channel set 92 toremain orthogonal to the in-phase channel set 90 and therefore to beprovided without adding additional interference to the other channelstransmitted over the same path with perfect receiver phase recovery.Thus, a complete set of sixty-four Walsh_(i) channels is added in anorthogonal manner to the original IS-95 channel set, and this channelset can be used for the supplemental channel. Additionally, byimplementing the supplemental channel in the orthogonal quadrature-phasechannel set 92, a subscriber unit 10 configured to process the normalIS-95 forward link signal will still be able to processes the IS-95channels within in-phase channel set 90 thus providing thehigh-transmission-rate channel while maintaining backwards compatibilitywith previously existing systems.

While the embodiment of the invention shown in FIG. 3 uses a single setof in-phase and quadrature-phase carriers to generate the in-phase andquadrature-phase channel set, separate sets of sinusoids could be usedto independently generate the in-phase and quadrature-phase channelsets, with the second set of carriers offset from the first set by 90°.For example, the D_(Q) data could be applied to the second set ofcarrier sinusoids where the D_(Q) in-phase (PNI) spread data is appliedto COS(ω_(c) t-90°) and the D_(Q) quadrature-phase (PNQ) spread data isapplied to SIN(ω_(c) t-90°). The resulting signals are then summed toproduce the quadrature-phase channel set 92, which in turn are summedwith the in-phase channel set 90.

The use of the Walsh_(S) channels as set forth in Table I. also allowssimplified implementation of the supplemental channel withinquadrature-phase channel set 92. In particular, the use of the Walsh_(S)codes listed in Table I allows the supplemental channel to use wholesubsets of 64 symbol Walsh_(i) codes without the need to generate eachand everyone of those Walsh codes.

For example, when N=5 the Walsh_(S) codes specified by Table I allocatea set of 32 64-symbol Walsh_(i) codes for the supplemental channel. Thatis, all the even-indexed 64-symbol Walsh codes or all of the odd-indexed64-symbol Walsh codes are allocated for the supplemental channel. Thisleaves the odd-indexed or even-index channels, respectively, forimplementing the extended IS-95 traffic channel set. In FIG. 3, thesupplemental channel uses the odd 64-symbol Walsh code channels whenWalsh_(S) ={+,-} and the even channels are available for the extendedIS-95 traffic channel set.

In another example, when N=4, the associated Walsh_(S) codes allocate aset of sixteen 64-symbol Walsh_(i) codes. This leaves a set offorty-eight remaining Walsh_(i) codes for implementing the extendedIS-95 traffic channels or for implementing additional supplementalchannels. In general, the use of the Walsh_(S) code that corresponds toa particular value N allocates 2^(N) 64-symbol Walsh_(i) codes for thesupplemental channel using only a single, and shorter, Walsh_(S) code.

The allocation of whole subsets of Walsh_(i) codes using a singleWalsh_(S) code is facilitated by even distribution the 64-symbolWalsh_(i) codes within the subset. For example, when N=5 the Walsh_(i)codes are separated by 2, and when N=4 the Walsh_(i) codes are separatedby 4. Only by providing a complete set of quadrature-phase channels 92for implementing the supplemental channel can the allocation of largeset of evenly spaced Walsh_(i) channels be performed, and thereforeimplemented using a single Walsh_(S) code.

Also, allocating a subset of 64-symbol Walsh_(i) codes using a singleshorter Walsh_(S) code reduces the complexity associated with providinga high-rate supplemental channel. For example, performing actualmodulation using the set of 64-symbol Walsh_(i) codes, and summing ofthe resulting modulated data would require a substantial increase insignal processing resources when compared with the use of the singleWalsh_(S) generator used in the implementation of the inventiondescribed herein.

Sets of evenly spaces Walsh_(i) channels could not be allocated aseasily if the supplemental channel were placed in the in-phase channelset 90 of the previously existing IS-95 forward link, or in the in-phaseand quadrature-phase channels with QPSK modulation. This is becausecertain sixty-four symbol Walsh_(i) channels are already allocated forcontrol functions such as the paging, pilot, and sync channels on thein-phase channel. Thus, using a new quadrature-phase Walsh code spaceallows for simplified implementation of the supplemental channel.

Also, the use of the a single Walsh_(S) code improves the performance ofthe high-rate supplemental channel because the variance in the amplitudeof the supplemental channel is minimized. In the embodiment describedherein, the amplitude is simply based on the positive or negativeinteger associated with the Walsh_(S) code. This is in contrast toperforming the modulation with a set of 2^(N) 64-symbol Walsh^(i) codes,which would result in the set of amplitudes 0, +2, -2, +4, -4, . . . ,2^(N), and -2^(N).

Among other improvements, reducing the variance in the amplitude reducesthe peak-to-average power ratio, which increases the range at which theforward link signal can be received for a given maximum transmit powerof the base station 12, or other forward link transmit system.

FIG. 5 is a block diagram of the supplemental channel system 132 of FIG.1 when configured in accordance with one embodiment of the invention.User data is received by CRC checksum generator 200 which adds checksuminformation to the data received. In the preferred embodiment of theinvention, the data is processed in 20 ms frames as is performed forIS-95, and 16 bits of checksum data is added. Tail bits 202 adds eighttail bits to each frame. The output of tail bits 202 is received at adata rate D by convolutional encoder 204 which performs convolutionalencoding at rate R_(c) on each frame. R_(c) differs for differentembodiments of the invention as described in greater detail below.

Block interleaver 206 interleaves the code symbols from convolutionalencoder 204 and repeater 208 repeats the code symbol sequence frominterleaver 206 by a repeat amount M. The repeat amount M varies indifferent embodiments of the invention, and will typically depend on thecoding rate R_(c) and the supplemental channel rate R_(S) (see FIG. 3).The repeat amount is discussed further below. Mapper 210 receives thecode symbols from repeater 208 and converts the logic zeros and logicones into positive and negative integer values which are output at thesupplemental channel rate R_(S).

Table II provides a list of data input rates D, encoding rates R_(c),repeat amounts M, and supplemental channel rates R_(S) that can be usedin different embodiments of the invention. In some embodiments multiplerates are used.

                                      TABLE II                                    __________________________________________________________________________    Convol- Walsh                                                                              Convol-  Walsh     Number of                                     utional Channels                                                                           utional  Symbols/                                                                           Convol-                                                                            Channel                                       Encoder for Supp.                                                                          Code                                                                              Repetition                                                                         Code utional                                                                            Bits                                          Input Rate                                                                            Channel                                                                            Rate                                                                              Amount                                                                             Symbols                                                                            Encoder                                                                            per                                           (D) kbps                                                                           (N)                                                                              (2.sup.N)                                                                          (R.sub.c)                                                                         (M)  (W/S)                                                                              Input Bits                                                                         Frame                                         __________________________________________________________________________    38.4 2   4   .sub.-- 1/2                                                                       1    16/1   768                                                                              1,536                                         38.4 3   8   .sub.-- 1/4                                                                       1    8/1    768                                                                              3,072                                         38.4 4  16   .sub.-- 1/4                                                                       2    4/1    768                                                                              6,144                                         38.4 5  32   .sub.-- 1/4                                                                       4    2/1    768                                                                              12,288                                        38.4 6  64   .sub.-- 1/4                                                                       8    1/1    768                                                                              24,576                                        76.8 3   8   .sub.-- 1/2                                                                       1    8/1  1,536                                                                              3,072                                         76.8 4  16   .sub.-- 1/4                                                                       1    4/1  1,536                                                                              6,144                                         76.8 5  32   .sub.-- 1/4                                                                       2    2/1  1,536                                                                              12,288                                        76.8 6  64   .sub.-- 1/4                                                                       4    1/1  1,536                                                                              24,576                                        153.6                                                                              4  16   .sub.-- 1/2                                                                       1    4/1  3,072                                                                              6,144                                         153.6                                                                              5  32   .sub.-- 1/4                                                                       1    2/1  3,072                                                                              12,288                                        153.6                                                                              6  64   .sub.-- 1/4                                                                       2    1/1  3,072                                                                              24,576                                        __________________________________________________________________________

Three encoder input rates D for the supplemental channel are shown:38.4, 76.8, and 153.6 kilobits per second. For each of these encoderinput rates D, a set of encoder rates R_(c), N values, and repeatamounts M are provided which achieve the desired encoder input rate D.Additionally, the ratio of Walsh_(S) symbols to code symbols isprovided, which corresponds to the length of the Walsh_(S) code. Also,the number of encoder input bits per 20 frame is provided, as is thenumber of code symbols transmitted per 20 ms frame. The actual datatransmission rate will be equal to the encoder input rate D, less theoverhead necessary for the CRC bits and tail bits and any other controlinformation provided. The use of Reed-Soloman encoding in addition to,or instead of, CRC checksum encoding is also contemplated.

In general, it is desirable to use the largest value of N possible forthe supplemental channel in order to spread the supplemental channelover the greatest number of Walsh_(i) channels. Spreading thesupplemental channel out over a larger set of Walsh_(i) channelsminimizes the effect of inter-channel interference between the twocorresponding Walsh_(i) channels on the in-phase channel set 90 and thequadrature-phase channel set 92. This inter-channel interference iscreated by imperfect phase alignment experienced during receiveprocessing. By spreading out the supplemental channel over a larger setof Walsh_(i) channels, the amount of inter-channel interferenceexperience for any particular Walsh_(i) channel in the in-phase channelset 90 is minimized, because the portion of the supplemental channel inthat Walsh_(i) channel is small. Also, spreading the supplementalchannel over a larger set of Walsh_(i) channels with a larger totalchannel symbol rate allows for a higher symbol diversity, which improvesperformance in fading channel conditions.

When the number of Walsh channels needed for the desired encoder inputrate D using rate 1/2 encoding is less than the number of availableWalsh channels by at least a factor of two, performance is improved byspreading the signal over more Walsh channels. The higher channel symbolrate for the larger number of Walsh channels is obtained by using a rate1/4, rather than a rate 1/2, code, or by sequence repetition, or both.The rate 1/4 code provides additional coding gain over that of a rate1/2 code in benign and fading channel conditions and the sequencerepetition provides improved performance in fading channel conditionsdue to the increased diversity.

In a preferred embodiment of the invention, a supplemental channelhaving an encoder input rate of 76.8 kilobits per second is providedusing N=5, an encoder rate R_(c) of 1/4, and a repetition amount of M=2.Such an implementation provides data transfer rates on the order of anISDN channel including sufficient bandwidth for signaling. Also, usingN=5 maintains 32 additional Walsh_(i) channels for providing extendedIS-95 channels.

The actual sustainable transmission rate of the supplemental channelwill vary depending on a variety of environmental conditions includingthe amount of multipath experienced by the forward link transmission.The supplemental transmission rate depends of the amount of multipathbecause forward link signals that arrive via different paths are nolonger orthogonal and therefore interfere with one another. Thisinterference increases with increased transmission rates because of theadditional transmit power necessary. Thus, the more multipathinterference experienced, the less the sustainable transmission rate ofthe supplemental channel. Therefore, a lower transmission rate for thesupplemental channel is preferred for high multipath environments.

In one embodiment of the invention, a control system that measures thevarious environmental factors and which selects the optimal supplementalchannel processing characteristics is contemplated. Also, the use ofsignal cancellation is contemplated for removing noise due to multipathtransmissions. A method and apparatus for performing such noisecancellation is described in copending U.S. patent application Ser. No.08/518,217 entitled "METHOD AND SYSTEM FOR PROCESSING A PLURALITY OFMULTIPLE ACCESS TRANSMISSIONS" assigned to the assignee of the presentinvention and incorporated herein by reference.

FIG. 6 is a block diagram of a receive processing system for processingthe high-rate supplemental channel in accordance with one embodiment ofthe invention. Typically, the receive processing system will beimplemented in a subscriber unit 10 of a cellular telephone system.

During operation, RF signals received by antenna system 300 aredownconverted with in-phase carrier 302 and quadrature-phase carrier 304generating digitized in-phase receive samples R_(I) and quadrature-phasereceive samples R_(Q). These receive samples are provided to the fingerprocessor module shown and to other finger processors (not shown) inaccordance with the use of a rake receiver. Each finger processorprocesses one instance of the supplemental forward link signal received,with each instance generated by multipath phenomena.

The in-phase and quadrature-phase receive samples R_(I) and R_(Q) aremultiplied with the complex conjugate of the PN spreading codesgenerated by in-phase spreading code generator 306 and quadrature-phasespreading code generator 308 yielding receive terms Y_(I) and Y_(Q). Thereceive terms Y_(I) and Y_(Q) are modulated with the Walsh_(S) codegenerated by Walsh generator 310, and the resulting modulated data issummed over the number of Walsh symbols in the Walsh_(S) code by summers312. Additionally, the receive terms Y_(I) and Y_(Q) are summed andfiltered (averaged) by pilot filters 316.

The outputs of summers 312 are then multiplied with the complexconjugate of the filter pilot data, and the resulting quadrature-phaseterm is used at the supplemental channel soft-decision data 320.Supplemental soft-decision data 320 can then be combined withsoft-decision data from other finger processors (not shown) and thecombined soft-decision data decoded.

FIG. 7 is a block diagram of decoder system used to decode thesupplemental soft-decision data 320 in accordance with one embodiment ofthe invention. The soft-decision data is received by accumulator 400which accumulates samples of the soft-decision data by the repeat amountM. The accumulated data is then deinterleaved by block deinterleaver 402and decoded by trellis decoder 404. Various types of decoders are wellknown including Viterbi decoders.

The user data in the hard-decision data from trellis decoder 404 is thenchecked with the CRC checksum data by CRC check system 406, and theresulting user data is output along with check results indicatingwhether the user data was consistent with the check sum data. Thereceive processing system or user can then determine whether to use theuser data based on the CRC checksum results.

Thus, a high data rate transmission system particularly suited for usein conjunction with the IS-95 forward link has been described. Theinvention can be incorporated into both terrestrial as well as satellitebased wireless communication systems, as well as wire basedcommunication systems over which sinusoidal signals are transmitted suchas coaxial cable systems. Also, while the invention is described in thecontext of a 1.2288 MHz bandwidth signal, the use of other bandwidths isconsistent with the operation of the invention including 2.5 MHz and 5.0MHz systems.

Similarly, while the invention is described using transmission rates onthe order of 10 kbps and 70 kbps, the use of other channel rates may beemployed. In a preferred embodiment of the invention, the varioussystems described herein are implemented using semiconductor integratedcircuits coupled via conduct, inductive, and capacitive connections, theuse of which is well known in the art.

The previous description is provided to enable any person skilled in theart to make or use the present invention. The various modifications tothese embodiments will be readily apparent to those skilled in the art,and the generic principles defined herein may be applied to otherembodiments without the use of the inventive faculty. Thus, the presentinvention is not intended to be limited to the embodiments shown hereinbut is to be accorded the widest scope consistent with the principlesand novel features disclosed herein.

We claim:
 1. A method for transmitting a high data rate channel inconjunction with a set of medium rate communications using code divisionmultiple access processing comprising the steps of:a) generating anin-phase set of medium rate channels; b) generating a quadrature-phaseset of medium rate channels; c) transmitting said set of high data ratechannel over said in-phase set of medium rate channels; and d)transmitting said high-rate communication over a subset of saidquadrature-phase set of medium rate channels.
 2. The method as set forthin claim 1 wherein said subset is comprised of a set of evenly spaceWalsh channels.
 3. The method of claim 1 wherein steps a) is comprisedof the step of:generating said set of channels by modulating said set ofmedium rate communications with a set of long channel codes; summingsaid set of channels yielding summed data; generating in-phase spreaddata in response to said summed data and an in-phase spreading code;generating quadrature-phase spread data in response to said summed dataand a quadrature-phase spreading code; modulating said in-phase spreaddata with an in-phase carrier yielding an in-phase signal; modulatingsaid quadrature-phase spread data with a quadrature-phase carrieryielding a quadrature-phase signal; and summing said in-phase signal andsaid quadrature phase signal.
 4. The method of claim 1 wherein steps b)is comprised of the step of:generating said high-rate channel bymodulating said high-rate communication with a short channel code;generating high-rate in-phase spread data in response to said high-ratechannel and said in-phase spreading code; generating high-ratequadrature-phase spread data in response to said high-rate data and aquadrature-phase spreading code; modulating said high-rate in-phasespread data with an quadrature-phase carrier yielding an high-ratequadrature-phase signal; modulating an inverted instance of saidhigh-rate quadrature-phase spread data with an in-phase-phase carrieryielding a high-rate in-phase-phase signal; and summing said high-ratein-phase signal and said high-rate quadrature phase signal.
 5. Themethod of claim 1 wherein steps a) and b) are comprised of the stepsof:a.1) modulating said set of medium rate communications using a set ofchannel codes; a.2) summing said set of channel codes yielding summeddata; a.3) modulating said summed data with a first set of carriersinusoids; b.1) modulating said high-rate channel with a short channelcode yielding said high-rate channel; and b.2) modulating said high-ratechannel with a second set of carrier sinusoids that are 90° out of phasewith said first set of carrier sinusoids.
 6. The method as set forth inclaim 5 wherein said short channel code is comprised of two Walshsymbols and said long channel codes are each comprised of sixty-fourWalsh symbols.